Truck and method of controlling electric drive motor for driving mounted on truck

ABSTRACT

When a stepping amount of an accelerator pedal is 0%, torque Ta is generated with the rotating speed being zero. When retreat is occurred in the slope start, the rotating speed is reduced. When the rotating speed is reduced, the torque is increased. Thus, the retreating force finally matches the propulsion force. As a result, the retreat becomes uniform motion. The decision of torque in such a manner does not require a value of a vehicle weight.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to Japanese Patent Application No.2017-126005, filed Jun. 28, 2017, the disclosure of which isincorporated by reference herein in its entirety.

BACKGROUND

The present disclosure relates to an electric motor-driven truck.

A driver of a vehicle changes step from a brake pedal to an acceleratorpedal when starting the vehicle on a slope. JP2014-166053A discloses atechnique that in order to prevent an electric motor-driven vehicle fromdescending and retreating on a slope during the changing step, torque isgenerated in accordance with the gradient amount of the slope.

The retreating force acting in a retreating direction on an uphill isinfluenced by not only the gradient amount of the slope but also avehicle weight. However, the disclosure in the prior art document doesnot mention the vehicle weight. It is considered that this is becausethe disclosure in the above technique is based on the assumption thatthe vehicle weight is nearly constant. When general passenger vehiclesare targeted, a problem would not be raised even based on suchassumption because the variation width of a vehicle weight is not large.

However, in the case of trucks, the variation width of a vehicle weightis considerably larger than the case of passenger vehicles due to aloaded freight amount. Thus, when the above-described assumption isadopted, the excess or shortage of torque may occur. Measuring orestimating a vehicle weight and considering a vehicle weight, it ispossible to use the method in the above technique. However, suchmeasurement or estimation requires time and effort or complicatedarithmetic operation. Thus, it is preferable to avoid such measurementor estimation.

Therefore, there is need facilitating an electric motor-driven truck tostart on a slope by an easy method.

SUMMARY

A first aspect provides a truck. The truck of the first aspect includesan electric drive motor for driving; and a control unit configured tocontrol the electric drive motor to generate, when retreat is occurredin slope start, torque in an opposite direction from torque acting onthe electric drive motor due to gradient of the slope, the toque havingan absolute value same as an absolute value of the torque acting due tothe gradient of the slope. In such an aspect, the retreat becomesuniform motion, which enables a driver to perform driving operationcalmly and facilitates slope start. Furthermore, a value of a vehicleweight is unnecessary to decide torque in the above-described manner,and thus it is easily achieved.

A second aspect provides a truck. The truck of the second aspectincludes a drive motor for driving; and a control unit configured tocontrol the electric drive motor, when retreat is occurred in slopestart, so that propulsion force generated by the electric drive motormatches retreating force generated due to the gradient of the slope. Insuch an aspect, it is possible to obtain the same effects as the firstaspect.

A third aspect provides a truck. The truck of the third aspect includesan electric drive motor for driving; and a control unit that controlsthe electric drive motor, when retreat is occurred in slope start, sothat the retreat becomes uniform motion. In such an aspect, it ispossible to obtain the same effects as the first aspect.

In the first to third aspects, when the retreat is occurred, an absolutevalue of the rotating speed of the electric drive motor increasesmonotonically as an absolute value of a speed increases by the retreat;and the control unit may increase torque generated by the electric drivemotor as the rotating speed is reduced from zero. In such an aspect, theretreat may become uniform motion without using a value of a speed.

In the first to third aspect, the control unit may perform control, whenthe torque is increased as the rotating speed is reduced from zero, sothat the torque increment is proportional to variation of the rotatingspeed. In such an aspect, the control is easier than PI control and thelike, and hunting hardly occurs.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic view of a truck.

FIG. 2 is a block configuration diagram of a power unit.

FIG. 3 is a graph illustrating the relation between torque and therotating speed.

FIG. 4 is a graph illustrating the relation between torque and therotating speed.

FIG. 5 is a graph illustrating the time change of vehicle speeds in theslope start.

DESCRIPTION OF EMBODIMENTS

FIG. 1 illustrates a truck 10. The truck 10 pulls a trailer 19. Thetruck 10 includes two power units 20, a propeller shaft 25, and anoperation system 900. The power units 20 have a function implementinggeneration of electric power by a fuel cell, as described later.

The operation system 900 is a generic term of devices operated by adriver for driving. The operation system 900 includes an acceleratorpedal 910, a brake pedal 920, a steering wheel (not illustrated), andthe like. Each of two power units 20 supplies electric power to theoperation system 900. The torque generated by two power units 20 istransmitted to four rear wheels RW through one propeller shaft 25.

FIG. 2 is a block configuration diagram of the power unit 20. The powerunit 20 includes a fuel cell module 50 and an electric system 60. Thefuel cell module 50 includes a fuel cell stack 100, a hydrogen tank 105,a converter for the fuel cell 110, and auxiliary machines 140. Theelectric system 60 includes a secondary battery 120, a converter for thesecondary battery 130, a motor inverter 150, a control unit 160, anelectric drive motor 220, and a resolver 230.

The hydrogen tank 105 stores hydrogen for supply to the fuel cell stack100. The fuel cell stack 100 is connected electrically to the converterfor the fuel cell 110. The converter for the fuel cell 110 performsboosting operation for increasing an output voltage of the fuel cellstack 100 to a target voltage. The converter for the fuel cell 110 isconnected electrically to the motor inverter 150 through high-pressureDC wiring DCH.

The secondary battery 120 is a lithium titanate secondary battery. Thesecondary battery 120 is connected electrically to the converter for thesecondary battery 130 through low-pressure DC wiring DCL. The secondarybattery 120 has a structure in which a plurality of cells are stacked inseries.

The converter for the secondary battery 130 is connected electrically tothe converter for the fuel cell 110 and the motor inverter 150 throughhigh-pressure DC wiring DCH. The converter for the secondary battery 130adjusts a voltage in the high-pressure DC wiring DCH that is an inputvoltage to the motor inverter 150, and controls charge and discharge ofthe secondary battery 120.

The converter for the secondary battery 130 discharges the secondarybattery 120 when the output electric power from the converter for thefuel cell 110 is smaller than target output electric power.

When regenerative electric power is generated by the electric drivemotor 220, the converter for the secondary battery 130 converts theregenerative electric power from AC to DC and outputs the regenerativeelectric power to the low-pressure DC wiring DCL side.

The converter for the secondary battery 130 is able to convert outputelectric power of the fuel cell stack 100 and output electric power tothe low-pressure DC wiring DCL side. Using the converted electric power,the control unit 160 is able to perform control of increasing SOC of thesecondary battery 120 when the electric power outputtable from theconverter for the fuel cell 110 exceeds the target output electricpower.

The auxiliary machines 140 is a generic term of auxiliary machines usedfor operation of the fuel cell stack 100. The auxiliary machines 140include an air compressor, a hydrogen circulation pump, a water pump,and the like. The auxiliary machines 140 are connected electrically tothe low-pressure DC wiring DCL or the high-pressure DC wiring DCH.

The motor inverter 150 converts DC power supplied through thehigh-pressure DC wiring DCH into three-phase AC power. The motorinverter 150 is connected electrically to the electric drive motor 220and supplies three-phase AC power to the electric drive motor 220. Themotor inverter 150 converts regenerative electric power generated in theelectric drive motor 220 into DC power and outputs it to thehigh-pressure DC wiring DCH.

The resolver 230 detects a rotation angle of a rotor in the electricdrive motor 220 and inputs the detection result to the control unit 160.

The control unit 160 includes a plurality of ECUs. The control unit 160controls operation of each part of the power unit 20, including theabove-described contents.

FIG. 3 is a graph illustrating the relation between torque defined foreach stepping amount of the accelerator pedal 910 and the rotatingspeed. Hereinafter, the merely-refereed stepping amount indicates astepping amount of the accelerator pedal 910. FIG. 3 illustrates thecases with the stepping amounts of 0%, 10%, and 20%. In actually, therelation with 0% to 100% is defined with intervals smaller than 10%.

The merely-referred torque in the embodiment indicates torque generatedby the electric drive motor 220. The merely-referred rotating speed inthe embodiment indicates the rotating speed of the electric drive motor220. The control unit 160 stores such relation as a map. The controlunit 160 controls the electric drive motor 220 based on the relationthrough the motor inverter 150.

FIG. 3 extracts and illustrates the case with the rotating speed ofaround 0 rpm. Actually, also regarding the larger rotating speed, therelation between the torque and the rotating speed is defined. Asillustrated in FIG. 3, even when the rotating speed is a negative value,the relation between the rotating speed and the torque is defined. Therelation when the rotating speed is a negative value is not applied tobackward driving such as in parking but the situations in which avehicle is retreated when starting on a slope. Even when the rotatingspeed is a negative value, the torque generates propulsion force in adirection allowing the truck 10 to travel forward as long as the torquevalue is positive.

The following will describe the slope start. To be more specific, thefollowing will describe the action of the truck 10 when it is stopped onan uphill while a driver steps the brake pedal 920 and then started oncethe driver stops stepping the brake pedal 920 and steps the acceleratorpedal 910.

When the tire is not span, the rotating speed and the vehicle speed arein proportional relation, in which when the rotating speed is zero, thevehicle speed is also zero. Furthermore, when the tire is not span, thetorque and the force for propelling a vehicle body are in proportionalrelation. The following description assumes that the tire is not span.

FIG. 4 is a graph illustrating the relation between the torque and therotating speed when the steeping amount is 0%. When the rotating speedis zero, a value of generated torque is torque Ta. When the rotatingspeed is reduced from zero, the torque increases linearly at a rate ofΔT/ΔR until reaching torque Tmax. That is, the rotating speed and thetorque are in proportional relation. Note that ΔR is regarded as apositive value. The increase of ΔR indicates the increase of an absolutevalue of ΔR. The expression that the rotating speed is reduced from zeroindicates that the rotating speed is a negative value and an absolutevalue of the rotating speed is increased.

FIG. 5 is a graph illustrating the time change of vehicle speeds in theslope start. FIG. 5 illustrates a case of a vehicle weight M1 and a caseof a vehicle weight M2. The vehicle weight M1 is a vehicle weight whenthe trailer 19 is not loaded with fright. The vehicle weight M2 is avehicle weight when the trailer 19 is fully loaded with freight, and isseveral times the vehicle weight M1. Time between time A and time C1 andbetween the time A and time C2 is time during which any of theaccelerator pedal 910 and the brake pedal 920 is not stepped (changingstep time).

A point A illustrated in FIG. 4 corresponds to the time A of FIG. 5. Thesame applies to the points B1, B2. As illustrated in FIG. 4, with thestepping amount of 0%, the torque generated at the time A is referred toas torque Ta, the torque generated at the time B1 is referred to astorque Tb1, and the torque generated at the time B2 is referred to astorque Tb2.

The time at the point A is time at which a driver stops stepping thebrake pedal 920. At the time of the point A, the vehicle speed is zero,as illustrated in FIG. 5. At the time of the point A, the steppingamount is 0%, and thus the torque corresponding to the rotating speed ofzero is generated, as illustrated in FIG. 4.

In the case of the vehicle weight M1, retreating force F1 acting in aretreating direction on an uphill is calculated by F1=M1·g·sin θ1 in asimplified manner. The g is gravity acceleration. The θ1 is an anglecorresponding to the gradient of a slope in the case of the vehicleweight M1. Also in the case of the vehicle weight M2, the retreatingforce F2 is calculated by F2=M2·g·sin θ2.

If the propulsion force generated by the torque Ta exceeds theretreating force F1, F2, the truck 10 travels forward. However, in theexample illustrated in FIG. 5, the propulsion force generated by thetorque Ta is smaller than the retreating force F1, F2. Thus, theacceleration in a retreating direction occurs.

When the acceleration in a retreating direction occurs, the rotatingspeed of the electric drive motor 220 becomes a negative value. As thespeed in a retreating direction increases, an absolute value of therotating speed is increased gradually. Thus, the torque is increasedgradually, as illustrated in FIG. 4.

As the torque is increased gradually, the acceleration in a retreatingdirection is reduced gradually, as illustrated in FIG. 5. Then, in thecase of the vehicle weight M1, the propulsion force by the torque Tb1generated at the time B1 matches the retreating force F1. When thepropulsion force matches the retreating force, the acceleration becomeszero. As a result, the retreat becomes uniform motion. To be morespecific, the retreating speed becomes constant with a speed V1, asillustrated in FIG. 5.

Also in the case of the vehicle weight M2, the propulsion force by thetorque Tb2 generated at the time B2 matches the retreating force F2. Asa result, the retreating speed becomes constant with a speed V2.

In the above-described uniform motion, the absolute value of the torquegenerated by the electric drive motor 220 is equal to the absolute valueof the torque generated by the retreating force.

In the case of the vehicle weight M1, the accelerator pedal 910 isstepped at the time C1, generating torque larger than the case in whichthe stepping amount is 0%. Thus, as illustrated in FIG. 5, forwardacceleration is generated, and then the vehicle speed becomes a positivevalue. Also in the case of the vehicle weight M2, the accelerator pedal910 is stepped at the time C2, generating forward acceleration.Thereafter, the vehicle speed becomes a positive value.

The flow of signals for achieving the above-described control isorganized and described as follows. The resolver 230 measures a rotationangle. The measured rotation angle is input to the control unit 160. Thecontrol unit 160 calculates the rotating speed based on the inputrotation angle. The control unit 160 refers to a map to determine torquebased on the measured rotation angle. The control unit 160 transmits aninstruction for achieving the determined torque to the motor inverter150. The motor inverter 150 allows a current to flow in the electricdrive motor 220 in accordance with the instruction.

In the embodiment described above, it is possible to obtain at least thefollowing effects.

In the changing step time, the acceleration in a retreating direction isreduced gradually and becomes uniform motion. Thus, a driver is able tocalmly perform stepping change from the brake pedal 920 to theaccelerator pedal 910 in the slope start.

The determination of torque during stepping change time does not requirea value of the vehicle weight, a value of the gradient, or a value ofthe vehicle speed. This facilitates the implementation. The main reasonswhy such an effect is obtained are that the retreating itself is notprevented but allowed and that it is used that the electric drive motor220, unlike an internal combustion engine, is able to generate apositive value of torque even when the rotating speed is a negativevalue.

The hunting of torque is suppressed during steeping change time. This isbecause the increment amount of the torque when the rotating speed isreduced from zero is ΔT/ΔR. In other words, the value of ΔT/ΔR isdefined so that the hunting of torque hardly occurs during steppingchange time. That is, when ΔT/ΔR is excessively large, the hunting oftorque occurs during stepping change time, easily causing the situationin which the acceleration does not smoothly become uniform motion.Meanwhile, when ΔT/ΔR is excessively small, it takes time until theacceleration becomes uniform motion, which makes a retreating speedexcessively high. In the embodiment, the value of ΔT/ΔR is defined to bewell-balanced.

In addition to the above, the hunting of torque is suppressed becausesimple proportional control is used. With the use of PI control, PIDcontrol, or the like, the hunting easily occurs depending on a controlparameter.

The disclosure is not limited to the above-described embodiments andexamples, and may be achieved with various configurations withoutdeparting from the scope of the disclosure. For example, the technicalfeatures in the embodiments and examples corresponding to the technicalfeatures of each aspect in the summary of the disclosure may beappropriately replaced or combined in order to solve a part or all ofthe above-described problems or achieve a part or all of theabove-described effects. When the technical features are not explainedas necessary in the specification, they may be deleted appropriately.For example, the followings are exemplified.

The truck may not be a type pulling a trailer. For example, it may be afull trailer or a dump truck.

The value of ΔT/ΔR may be larger to such a degree that the hunting oftorque is generated. In this case, it is possible to reduce a retreatingspeed.

It is possible to measure a retreating speed and perform feedbackcontrol on the electric drive motor so that the variation of measuredvalues is zero.

It is possible to measure retreating acceleration and perform feedbackcontrol on the electric drive motor so that the variation of measuredvalues is zero.

The truck may not be a fuel cell vehicle. For example, it may be anelectric vehicle charging a secondary battery from a commercial electricpower source, or electric power generated by power of an internalcombustion engine may be supplied to the electric drive motor.

The truck may be a connected car. The connected car is a vehicle with acommunication device, capable of receiving service through communicationwith cloud.

The control for achieving retreat in uniform motion may not be mapcontrol. For example, it may be PI control. The PI control is able tochange ΔT/ΔR, that is, torque increment gradient. To be more specific,the control may be as follows. With addition of a correction termincreasing proportional control (P control) when the acceleration at thestart of retreat exceeds a reference value, such a correction term is ofintegration correction (I control). The integration correction term maybe kept to be a constant value in one-time slope start. The integrationcorrection term may be gradually reduced during traveling in one-timetrip. The integration correction term may be zero as long as thegradient of a slope is within a reference value. The integrationcorrection term may be kept in repeated start when the gradient islarger than a reference value. The integration correction term may berestored to an initial value when the traveling time is long or a tripis finished. This prevents hunting.

What is claimed is:
 1. A truck, comprising: an electric drive motor fordriving; and a control unit configured to control the electric drivemotor to generate, when retreat is occurred in slope start, torque in anopposite direction from torque acting on the electric drive motor due togradient of the slope, the torque having an absolute value same as anabsolute value of the torque acting due to the gradient of the slope. 2.A truck, comprising: an electric drive motor for driving; and a controlunit configured to control the electric drive motor, when retreat isoccurred in slope start, so that propulsion force generated by theelectric drive motor matches retreating force generated due to gradientof the slope.
 3. A truck, comprising: an electric drive motor fordriving; and a control unit configured to control the electric drivemotor, when retreat is occurred in slope start, so that the retreatbecomes uniform motion.
 4. The truck in accordance with claim 1, whereinwhen the retreat is occurred, an absolute value of rotating speed of theelectric drive motor increases monotonically as an absolute value of aspeed increases by the retreat, and the control unit increases torquegenerated by the electric drive motor as the rotating speed is reducedfrom zero.
 5. The truck in accordance with claim 2, wherein when theretreat is occurred, an absolute value of rotating speed of the electricdrive motor increases monotonically as an absolute value of a speedincreases by the retreat, and the control unit increases torquegenerated by the electric drive motor as the rotating speed is reducedfrom zero.
 6. The truck in accordance with claim 3, wherein when theretreat is occurred, an absolute value of rotating speed of the electricdrive motor increases monotonically as an absolute value of a speedincreases by the retreat, and the control unit increases torquegenerated by the electric drive motor as the rotating speed is reducedfrom zero.
 7. The truck in accordance with claim 4, wherein the controlunit performs control, when the torque is increased as the rotatingspeed is reduced from zero, so that the torque increment is proportionalto variation of the rotating speed.
 8. The truck in accordance withclaim 5, wherein the control unit performs control, when the torque isincreased as the rotating speed is reduced from zero, so that the torqueincrement is proportional to variation of the rotating speed.
 9. Thetruck in accordance with claim 6, wherein the control unit performscontrol, when the torque is increased as the rotating speed is reducedfrom zero, so that the torque increment is proportional to variation ofthe rotating speed.
 10. A method of controlling an electric drive motorfor driving mounted on a truck comprising: detecting occur of retreat inslope start; and controlling the electric drive motor to generate torquein an opposite direction from torque acting on the electric drive motordue to gradient of the slope, the torque having an absolute value sameas an absolute value of the torque acting due to the gradient of theslope.
 11. A method of controlling an electric drive motor for drivingmounted on a truck comprising: detecting occur of retreat in slopestart; and a control unit configured to control the electric drive motorso that propulsion force generated by the electric drive motor matchesretreating force generated due to gradient of the slope.
 12. A method ofcontrolling an electric drive motor for driving mounted on a truckcomprising: detecting occur of retreat in slope start; and a controlunit configured to control the electric drive motor so that the retreatbecomes uniform motion.